1. Field of the Invention
The present invention relates to novel viscoelastic viscosurgical materials and ophthalmic surgical techniques utilizing the materials.
2. Prior Art
In ophthalmic surgical procedures such as intraocular lens implantation, cataract surgery, retinal detachment repair, etc., there exists a need for viscous, gel-like compositions to fill the chambers of the eye to protect sensitive tissue such as the corneal endothelium from trauma. See U.S. Pat. No. 4,141,973; Pruett et al, Arch. Ophthalmol., 97:2325 (1979); Holmberg et al, Ophthalmology, 91:45 and 53 (1984); Pape et al, Ophthalmology, 87:669 (1980); MacRae et al, Am. J. Ophthalmol., 95:332 (1983); and Miller et al, Annals Ophthalmol., 13:811 (1981).
The most commonly employed materials are solutions of hyaluronic acid (HA), chondroitin sulfate (CS) and methylcellulose (MS); HA being the most widely used. However, HA is extrememly expensive. Furthermore, it requires extraordinary purification to remove as much proteinaceous immunogenic material as possible but still may provoke immune reactions in some patients. The use of HA and all other currently available viscosurgical materials for ophthalmic surgery is also often accompanied by significant undesirable intraocular pressure (IOP) rise which necessitates washing from the eye at the end of surgery and may also require antiglaucoma therapy. Even though HA is normally irrigated from the eye following its use in ocular surgery, transient potentially hazardous episodes of IOP rise have been known to occur.
Sterilization and shelf-life stability are other problems associated with HA and other currently available materials. They are subject to significant degradation by thermal or radiation sterilization methods making safe sterile processing difficult and expensive. Ambient temperature instability also necessitates refrigerated shipment and storage. In contrast, the materials of the present invention are far more stable, may be readily autoclave sterilized without degradation and may be stored at room temperature safely for long periods of time.
It has also been suggested to employ an aqueous solution of high molecular weight carboxymethylcellulose (CMC) as a viscosurgical material. U.S. patent application Ser. No. 903,445, filed Sept. 4, 1986, discloses the use of a solution of high molecular weight carboxymethylcellulose as an ophthalmic viscoelastic surgical material. Although CMC represents a significant improvement over other known viscosurgical materials, especially in ease of purification and lower cost, its use may still be accompanied by some transient IOP rise following surgery.
It is an object of the present invention to provide improved ophthalmic viscoelastic surgical materials and ophthalmic surgical techniques embodying same which are far less subject to the above-noted disadvantages.